The three missing men were identified as Clancy Nichols, 51, his son Danny Nichols, 24, and Wes Hawkins, 46.
Mesa County officials say the mudslide is 2 miles wide and 4 miles long. Deputies describe the area as very unstable, and estimate that an entire ridge was sliding for most of Sunday.
"This slide is unbelievably big," said Lt. Phil Stratton with the Mesa County Sheriff's Office.
"Massive is an understatement," said Mesa County Sheriff Stan Hilkey on Monday. He said the three men were sent up to investigate disrupted irrigation. They were traveling in a vehicle and a 4-wheeler when a second mudslide occurred.
Hilkey said the search has been hampered because only the lower third of the slide is stable. At the edges there, the mud is 20 to 30 feet deep.
Hilkey said everyone is praying for a miracle but said no signs of the men or their truck have been found.
He has consulted with the sheriff who responded to March's mudslide in Washington state for advice on how to handle the search.
"I know (the missing are) residents of what we call the Collbran-Mesa area," said Heather Benjamin with the Mesa County Sheriff''s Office.
"Those are two small towns up there on the Grand Mesa, which to us would typically indicate that they're familiar with the terrain. They're probably very outdoorsy, probably very prepared for the severe weather and being stuck in the mountains overnight, and those kinds of things."
The first reports of the mudslide came into the Grand Junction Regional Communication Center about 6:15 p.m. Sunday.
The Plateau Valley Fire Department responded to the area just east of the small town of Collbran after a witness called into dispatch after hearing a noise that sounded like a freight train that is attributed to the slide. Collbran is about 40 miles east of Grand Junction.
The area is very remote and no structures have been reported damaged so far. I-70 is approximately 26 miles north of the slide and has not been affected.
Rain fell in Mesa County most of Sunday and probably contributed to the cause of the slide. Officials urged citizens not to go into the area. A road block has been established at the intersection of Highway 330 and Salt Creek Road, outside the town of Collbran for safety.
Contributing: The Associated Press